Comparative shrinkage behavior of ultra-high-performance fiber-reinforced concrete under ambient and heat curing conditions

This study aims to investigate the effect of curing conditions on the free shrinkage behaviors of ultra-high-performance fiber-reinforced concrete (UHPFRC). For this study, a number of exposed and sealed prismatic UHPFRC samples for drying and autogenous shrinkage measurements were fabricated and tested using two different types of embedded strain gauges. Several other tests, including mechanical tests, X-ray diffraction (XRD), and mercury intrusion porosimetry analyses, were also performed. Test results indicate that steam curing with heat (90 °C, referred to as heat curing) was effective to improve the mechanical properties of UHPFRC at an early age in terms of strength, elastic modulus, and fracture energy absorption capacity. The larger quantities of C-S-H and much smaller total cumulative pore volume were obtained for the steam-cured specimens, compared to those for the ambient-cured specimens. The ultimate autogenous shrinkage of UHPFRC was insignificantly affected by the curing conditions, whereas heat curing accelerated the shrinkage development as compared to ambient curing. In particular, there was no increase of shrinkage strains for UHPFRC after heat curing was finished. The ultimate drying and autogenous shrinkage of UHPFRC were found to be approximately −45 με and −450 με, respectively. Based on literature review, an optimized model was suggested, and the autogenous shrinkage developments of UHPFRC at both ambient and heat curing conditions were successfully predicted based on the equivalent age method.